First of all, this depends on the cat. Some cats hold reductions, regardless when they did it, some don't. Second, even in cats that don't hold such reductions, it'd depend how low they go. A dip to upper 40's is different than a visit below 40, where we'd take a reduction regardless.
There are some explanations about why numbers differ from cycle to cycle in the Sticky Note:
What is the Insulin Depot?
Actually no. The rule on TR for earning reductions for long term diabetics is 1 time under 40 or a week in normal green numbers. For cats that do no hold reductions well, some people choose to follow the three times between 40 and 49 on 3 separate days, or once under 40. More details on reductions here:
Reminder: *earning* reductions and starting OTJ trials
It's possible you did a furshot, or had a drop on the needle from when you squeezed out some excess before shooting. Depend whether a light smell or a lot. And I found the smell stuck around at least a day.
With nadirs in the 80's and above, you probably have some room for an increase. Personal experience with Neko told me she needed to have nadirs in the 70's or lower, or she'd bounce a lot more. Of course, ECID.